ppc4xx: Enable 440 GPIO init table CFG_440_GPIO_TABLE for 405 platforms

- Rename CFG_440_GPIO_TABLE to CFG_4xx_GPIO_TABLE
- Cleanup of the 4xx GPIO functions
- Move some GPIO defines from the cpu headers ppc405.h/ppc440.h into gpio.h

Signed-off-by: Stefan Roese <sr@denx.de>